Friction element and method of improving the same



Patented Aug. 21, 1934 OFFICE FRICTION ELEMENT AND. METHOD or. mmovmeTHE SAME Izador J. Novak, Bridgeport, -Conn., assignor toRaybestos-Manhattan, Inc., Bridgeport, Conn., a corporation of NewJersey No Drawing. {A plication Serial No; 608,871

May '2, 1932,

4 Claims. (01. 91-68) This invention relates to friction elements andmethod of improving same, especially with respect to the removal ofcertain undesirable constituents in such elements.

In its broad aspects, the invention is directed to woven and unwovenelements, either rigid or flexible, and inone specific aspect, theinvention is particularly adapted to improvement of flexible woven brakelinings containing oxidized drying oil as a binder.

Of the several types of flexible brake linings on the market up to thepresent time, one of the most popular and generally serviceable typeshas been a woven asbestos base containing oxi- 18 dized drying oils asthe principal constituents of the binder. This combination providesbrake lining having satisfactory durability and a mode rately highcoefficient of friction, smooth action, and relative ease ofmanufacture. For these rea- 20. sons, a large proportion of servicebrake linings has consisted of this type of lining. A drawback, however,has been a marked tendency of such oil-treatedasbestos brake linings toexhibit an extremely low frictional coefiicient when thoroughly wet anda considerably higher than normal frictional coeflicient when damp. Inregions where precipitation is high, the sales of this type of brakelining, in spite of its normally excellent qualities, have not beencomparable withsales of other types.

I have found, after extended investigation, that all brake liningscontaining any considerable proportion of drying oil in the binder actin a similar manner, especially when used on external brakes where thelining is exposed to dampness and wetness. On analysis, I have foundthat such brake linings reveal a considerable proportion of free fattyacids and magnesium soaps of these fatty acids. These fatty acidscomprise, linolic,

linolenic, eleostearic and pyrogenetic on oxidation breakdown productsof these such as propionic acid.- Cotton tape treated with drying oilsand the drying oils dried therein show a free fatty acid content but, ofcourse, no magnesium soaps. It seems, therefore, that the free fattyacids are formed during the drying of the oil and that the magnesia inthe asbestos combines therewith to form magnesium soaps.

. According to the present invention, I have found. that, on extractinga drying oil-treated asbestos base brake lining with solvents as, for Iexample, alcohol or acetone, capable of dissolving magnesium soaps, theextracted brake lining when put into service on an external brake showsvery much greater resistance to change from the tracted tape as againstthe unextracted tape.

normal in damp or wet conditions. On further heating of such anextracted brake lining, a small proportion of free fatty acids andmagnesium .soaps is again formed but in so small a prois from 12% and20% of the supposed dried oil,

the magnesium soap comprising about threequarters of the extractedmatter. It will be appreciated thata quantity of soapy material of thenature of magnesium soap will exert a pronounced effect on the action ofbrake lining when wet, all the more aggragated by the fact that whilemagnesium soap becomesslimy when rubbed out while thoroughly wet, itdoes not dissolve completely in water and wash away as would, forexample, sodium soap. On removal of the soap by suitable solvents,further heating changes less than 2% of the total binder to soaps andacids.

In one preferred form of carrying out the invention, brake lining whichhas been treated with a saturant containing a drying oil and the dryingoil cured therein by oxidation, is placed in an extraction apparatus andexposed to hot methyl alcohol in an apparatus similar in design to theconventional Soxhlet extraction apparatus used in chemical laboratories.After several cycles of solvent replacement have taken place, the liningis removed from the extraction apparatus and the alcohol still remainingtherein is dried out in a suitable apparatus which may be equipped forrecovery of the solvent. The lining is then ready for use and exhibits amarkedimprovement over un-extracted material having the same preliminarytreatment. As an evidence of this, the extracted material showed on oneparticular car a deceleration of 14 feet per second per second at 80pounds pedal pressure, whereas, unextracted material shows an average ofonly 41 feet per second under the same conditions. Both these tests weremade overa period of ten hours'during which time the car lined with thebrake lining under test was run continuously throughdriving rain.

Furthermore, dampness results in an undesirable increased friction;especially on cold damp 'mornings- Under similar conditions, thefriction was decidedly better in the case of the exj Some of thesolvents which may be used for the removal of free fatty acids andmagnesium effecting such a removal. This operation for the advantagesobtained therefrom may also be carried out on unwoven brake linings andclutch facings where it is found that the presence of soaps or freefatty acids is not desirable.

Furthermore, the removal of undesirable'fatty or lubricating oilymaterial is valuable in the caseof friction materials which ordinarilyhave a marked tendency to fade or drop off in frictional coeflicient athigh temperatures, or under severe abuse, especially on cast iron drums.It will be appreciated that high temperatures cause such lubricatingoils to distil to the friction surface 'and thus reduce friction at thesurface. This is thecase with unwoven brake linings containing vegetableoils as modifiers of phenolic resin, for example, the loose fatty acidor soap or other decomposition products while generally lower inquantity than in the case of woven brake linings still are present insufficient proportion to produce such undesirable frictional effects asI have indicated. Extraction of these undesirable lubricants reducesfading and improves the action of the friction material. The extractionmay be carried out as in the case of woven brake Other undesirablelubricating organic matter which may have been introduced as anunavoidable constituent of the'saturant, or produced during thehardening of the saturant may be removed by extraction with a suitablesolvent in the same manner and for similar purposes to that describedabove.

I claim as my invention:

1. In the manufacture of friction elements wherein an asbestos base issaturated with a saturantcomprising drying oil andcured, the improvementwhich comprises extracting free fatty acids and magnesium soaps bysubjecting said base to the action of a solvent capable of removing suchfatty acids and magnesium soaps.

2. A process of improving friction brake lining comprising an asbestosbase and a suitable binder whereby the frictional coefficient thereofwill be substantially the same in wet or dry weather, which consists inextracting free fatty acids and magnesium soaps normally present in saidlining by subjecting the lining to the action of a solvent capable ofdissolving said fatty acids and magnesium soaps and then removing thesolvent.

3. In the manufacture of friction elements wherein an asbestos base issaturated with a saturant comprising drying oil and cured, theimprovement which comprises extracting free fatty acids and magnesiumsoaps normally present in said cured base by subjecting said basesubsequent to curing to the action of a solvent capable of removing suchfatty acids and magnesium soaps. 1

4. Brake lining comprising an asbestos base and a binder comprising thedried residue obtained from the hardening of a vegetable drying oil to acondition suitable for brake lining, wherein the percentage-of freefatty acids and magnesium soaps has been reduced by extraction to lessthan ten percent of the weight of the dried oil.

IZADOR J. NOVAK.

